FIELD OF THE INVENTION
The present invention relates to switching laser beams out of laser cavities, and more particularly, it relates to the use of generating harmonics of the laser beam to accomplish the switching.
when laser light is generated in a laser cavity the problem arises of how to switch the laser light out of the cavity in order to make use of the resulting laser beam in a well known multitude of ways. These uses include range finding, communication, remote sensing, medical surgery, laser fusion applications and many more. The switch-out problem becomes more difficult as the size of the laser aperture grows such as in laser fusion applications. The final amplifier stages of the Nova and Novette lasers at Lawrence Livermore National Laboratory are 46 centimeters with the laser beam expanded to 74 centimeters thereafter. Larger aperture lasers are planned.
In order to cut capital costs and simplify operation by cutting down on the number of optical components and associated equipment needed in large aperture lasers, laser fusion laser designers have decided to add energy to the laser beam by use of multiple passes of the laser beam through the same amplifier. These "multipass" laser system architectures include regenerative oscillators. The regenerative oscillator must employ a switch of some kind to get the laser beam out of the laser cavity. As the aperture size grows, the switching options in the art become more limited. An example of these switch designs is shown in Lawrence Livermore National Laboratory Report No. UCRL-53344 (1982) at pages 32-35. In particular, FIG. 39 (b) and (d) of UCRL-53344 display switchout through the use of a polarization change and through second harmonic conversion, respectively. It can be seen at page 33 that Pockels cells are specifically named for the FIG. 39 (b) switch. with respect to the FIG. 39, the second harmonic conversion takes place due to an intensity being reached in the laser light as it is amplified such that the second harmonic conversion takes place automatically. Angular sequencing is also mentioned.
Electro-optics and harmonic generation are well understood in the art as exemplified in the standard reference by F. Zernike and J. Midwinter, Applied Nonlinear Optics, John Wiley & Sons, N.Y., 1973 and the standard textbook by Amnon Yariv Introduction to Optical Electronics, Holt, Rinehart and Winston, Inc (New York 1971). Yariv is hereby incorporated by reference. The second harmonic generation discussion starts at page 189 and includes a description of second harmonic generation inside a laser resonator starting at page 194. Zernike and Midwinter is hereby incorporated by reference.
The problems in the art with respect to switching of large aperture laser systems remain difficult. In particular, the second harmonic generation described above in UCRL-53344 is dependent on the level of the fundamental intensity to achieve second harmonic generation conditions. Waiting until an appropriate intensity is reached means that some of the laser light will "leak" through the switching arrangement before other portions. This pre-pulse leakage not only represents a loss of energy but for applications such as laser fusion could result in damaging the target before the main laser pulse arrives. Therefore, a sharper-acting switch is needed.